Actin-depolymerizing factors 8 and 11 promote root hair elongation at high pH

Root hair is a polarly elongated single-celled tissue that derives from root epidermal cell for uptake of water and nutrient from the surrounding environment. Previous reports have demonstrated that short periods of high pH inhibited root hair extension, however, the effects of long-term high-pH treatment on the growth of root hairs is still unclear. Here, we reported that duration of root hair elongation is significantly prolonged with increasing external pH, which counteracts the effect of decreasing root hair elongation rate and ultimately produces longer root hairs, whereas loss of actin-depolymerizing factors 8 and 11 (ADF8/11) function causes shortening of root hair length at high pH (7.4). The accumulation of ADF8/11 at the tips of root hairs is inhibited by high pH and the increasing of environment pH impacts the actin filament (F-actin) meshwork at the root hair tip. At high pH, the tip-focused F-actin meshwork of adf8/11 mutant root hairs are absent, and actin filaments at the adf8/11 root hair tips are disordered accompanied with attenuated actin turnover. Furthermore, secretory and recycling vesicles in adf8/11 root hairs could not be aggregated in the apical region of root hairs at high pH. Together, our results suggest that under long-term exposure to high extracellular pH, ADF8/11 may establish and maintain the tip-focused F-actin meshwork to regulate the polar trafficking of secretory/recycling vesicles at the root hair tips, thereby promoting the elongation of root hairs.